As a method for imparting water/oil repellency and stain proofing property to the surface of a fiber product, etc., a method of treating an article with a water/oil repellent composition composed of an emulsion having a fluorinated copolymer having a polyfluoroalkyl group (hereinafter referred to as a Rf group) dispersed in an aqueous medium has been known.
As a method for treating a fiber with a water/oil repellent composition, the Dip-Nip method is generally employed. That is, it is a method such that an open-shape fabric (raw fabric) is dipped in a treating bath and then squeezed by a roller, followed by carrying out a drying step at an ambient temperature or by heating and an adhering step to prepare a treated fabric.
As a phenomenon which impairs the productivity of a water/oil repellent treatment on a fabric, it sometimes occurs that emulsion particles in a water/oil repellent agent are broken by mechanical impact in a treating bath or by anionic impurities derived from a fabric, and they aggregate to be coarse particles (hereinafter referred to as “scum”). Such coarse particles are brought to a squeezing roller by the fabric being treated and deposited on the squeezing roller (hereinafter referred to as “gum up”). If scum deposits on a squeezing roller, scum is transferred onto the treated fabric, which may sometimes result in stain on the fabric or irregular treatment on the treated fabric. Further, in order to clean scum deposited on the squeezing roller, the treatment step is interrupted, and thereby the productivity is lowered.
Further, in recent years, biological accumulation of Rf groups having at least 8 carbon atoms, for example pentafluorooctanesulfonic acid, is problematic, and a water/oil repellent composition having an Rf group having at most 6 carbon atoms has been proposed (Patent Document 1). However, in the case of a water/oil repellent composition comprising a copolymer having an Rf group having at most 6 carbon atoms, the frequency that scum is formed is high, since the crystallinity of the Rf group in a side chain is low. As a result, gum up may result. Further, scum having a strong adhesion is formed, since the crystallinity is low. As a result, a squeezing roller becomes very sticky, and thereby it is necessary to spent labor for cleaning.
In order to overcome the above problem, a water/oil repellent agent having excellent stability against impurities has been proposed (Patent Document 2). However, practically, surplus treating bath after squeezing by a squeezing roller is reused, and it is thereby difficult to completely suppress the occurrence of scum. Thus, scum gradually increases, and finally gum up results.